What is the tense of the underlined verb?

a. future
b. future perfect
c. future progressive
d. future perfect progressive

If the underlined verb is will have been talking, in the sentence Lillian will have been talking for two hours by the time she finishes her classical music lecture, then the correct answer is D. future perfect progressive.
A would be - will talk.
B would be - will have talked.
C would be - will be talking. 

The speed of  sound:   sound travels  at different speeds depending on what it istraveling through. of the three mediums (gas, liquid, and solid)  sound waves travel the slowest through  gases, faster  through  liquids, and fastest  through  solids.